Spider silk

materials science

1. SPIDER SILK PRESENTED BY PINTU MAITY M.Sc 2 ND SEM DEPARTMENT OF MATERIALS SCIENCE Roll No.-12

2. Spider silk is a protein fiber spun by spiders. Spiders use their silk to make webs or other structure which functions as sticky nets to catch other animals, or as nests or cocoons to protection their offspring. They can also suspended themselves using their silk. DEFINiTION

3. COMPOSITION OF SPIDER SILK The dragline  silk  of the Golden Orb-Weaving  spider  is the most studied in scientific research.  Spider silk  is a natural polypeptide, polymeric protein and is in the scleroprotein group such as collagen (in ligaments) and keratin (nails and hair). These are all proteins which provide  structure .

4. The protein in dragline  silk  is fibroin which is a combination of the proteins spidroin-1 and spidroin-2. The exact composition  of these proteins depends on factors including species and diet. Fibroin consists of approximately 42% glycine and 25% alanine as the major amino acids. A female specimen of  Argiope bruennichi   wraps her prey in silk. A  garden spider  spinning its web

5. TYPEs oF SPIDER SILK There are seven types of silk produced by seven silk glands.  A single spider does not possess all seven glands but has at least three if it is male (dragline, attachment and swathing silk) or four if it is female.  The additional one is for egg sac silk. 

6. Achniform gland : swathing silk. Cylindriform gland : egg sac silk. Ampullate glands (major and minor) : non-sticky dragline silk .  Silk from the minor ampullate gland is only half as strong as that from the major gland. Pyriform gland : attaching threads - attachment discs are made which anchor a thread to a surface or another thread. Flagelliform gland : core fibers of sticky silk. Aggregate gland : outer part of sticky silk - droplets of an adhesive substance are deposited along the threads.

7. The glands are located on the lower side of the abdomen (see diagram below) and contain a watery fluid known as 'dope'.  This fluid passes through to the spinneret via a multitude of microscopic tubes where water recovery and solidification begins.  Fluid from different glands can lead to the same spinneret so silk with specific properties required for a particular function can be produced.  There are usually three pairs of spinnerets but this can vary between 1 and 4 pairs depending on the species.  The substance exits through the spigots which are mobile, finger-like protrusions and the resulting silk emerges as a solid.  There are many spigots so many fibres are bound together like a cable.  The diameter of a single fibre is controlled by the muscular action of a valve.  The faster and tighter the strand is drawn, the stronger the silk.   .   HOW DO SPIDER PRODUCE SILK?

8. HOW do COLLECT THE SILK FROM SPIDER ? Using the silk extraction machine , we collect the spider silk . However the production of spider silk is not simple and there are inherent problems.   Firstly, spiders cannot be farmed like silkworms since they are cannibals and will simply eat each other if in close proximity.  The silk produced is so fine that 400 spiders would be needed to produce only one square yard of cloth.  The silk also hardens when exposed to air which makes it difficult to work with.

9. So, Biological Scientists , they are discovered a alternative approach. More recently, Nexia Biotechnologies Inc in Montreal, Canada have inserted silk genes into goats to produce silk proteins in their milk.  This is hoped to be a better method because protein from bacteria is not as strong due to faulty cross-linking of the proteins and hard white lumps can form.  Milk production in mammary glands is similar to silk protein production in spiders so it is thought that proper protein cross-linking could occur in goats. A MODERN APPROCH

10. MALE FEMALE

11. Most silks, in particular dragline silk, have exceptional mechanical properties. They exhibit a unique combination of high  tensile strength  and extensibility ( ductility ). This enables a silk fibre to absorb a lot of energy before breaking ( toughness , the  area under  a stress-strain curve). MECHANICAL PROPERTIES

12. Strength: In detail a dragline silk's  tensile strength  is comparable to that of high-grade alloy  steel  (450 - 2000 MPa ) and about half as strong as  aramid  filaments, such as  Kevlar (3000 Mpa ). Energy density The  energy density  of dragline spider silk is roughly 1.2x10 8 J/m 3 . Extensibility Silks are also extremely  ductile , able to stretch up to five times to their relaxed length without breaking . Spider silk is able to keep its strength below -40°C. The toughest silk is the dragline silk from the Golden Orb-Weaving spider ( Nephilia clavipes ). THERmal poperties

13. Toughness The combination of strength and ductility gives dragline silks a very high  toughness  (or work to fracture ). Supercontraction When exposed to water, dragline silks undergo supercontraction, shrinking up to 50% in length and behaving like a weak rubber under tension .

14. Kevlar VS. Spider dragline silk

15. Artificial Tendon/Ligament: Biocompatibility of spider silk, and the unusual characteristics of the stiffness/stretchiness combination has scientists considering its use for tendon and ligament repair in humans. Candidates for a tendon/ligament replacement must meet the requirements of strength to withstand regular impact and pressure, as well as avoiding fatigue during regular use.   Malfunctioning of parachute straps: The use of the silk’s tensile strength could be incorporated in parachute straps, to deter the chances of malfunctioning straps, and increase safety. Recreational and Industrial uses : For recreational and industrial uses, biodegradable fishing lines composed of spider silk would resist snapping under the force of a large biting fish. Also it’s potential use in instrument fibres for violins and cellos.   Idea of body armor : The idea of body armor woven from dragline silk, has been hypothetically observed. In the biological environment, 70% of the kinetic energy from a prey flying into a spider’s web is absorbed as heat and dissipated. With this background information, it can be conveyed that with the use of engineered spider silk the shock a person would feel from a bullet could be considerably reduced. USES OF SPIDER SILK

16. FUTUre steps In the future, the scientists plan to incorporate the silk  genes  into alfalfa plants, which they say could produce even larger quantities of silk. They explain that not only is alfalfa widely distributed, it also has a high (20-25%) protein content, making it an ideal crop to produce silk protein.

17. REFERENCES https://phys.org/news/2010-05-scientists-goats-spider-silk.html#jCp https://spider-silk.wikispaces.com

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